KNOXVILLE, Tennessee (CNN) --Gearing up for an election-year fight over the centerpiece of his education agenda, President Bush hailed his "historic" No Child Left Behind Act Thursday and announced he will seek a substantial increase in its funding for 2005.

Speaking to a group of educators and supporters at an elementary school in Knoxville, Bush called the act, which he signed into law two years ago Thursday, "a great piece of legislation which is making a difference around our country."

White House spokesman Scott McClellan told reporters Bush's 2005 budget proposal calls for an increase of more than $2 billion for elementary and secondary education, a 48 percent boost over 2001.

That announcement seemed a clear effort to counteract fierce criticism on the education front. Many leading Democrats, including some who helped pass the measure two years ago, have lambasted Bush for forcing schools to meet certain testing standards without giving them the resources to do so.

Several have said Bush's 2004 budget under funds the act by $9 billion.

The No Child Left Behind Act requires unprecedented testing of students. Schools that don't meet federal standards for improvement after five years could be restructured -- a move that could include firing some or all of the staff.

Bush, speaking at Westview Elementary School before a fund-raising event, said the act is yielding concrete results. "The fourth-grade math test scores around the nation are up nine points since 2000," he said. "The eighth-grade math scores are up five points. ... Reading tests are increasing for fourth-graders. We're making a difference."

Bush said that in the past, the federal government would send money to local schools "and hope something happened." The No Child Left Behind Act, he said, is "historic because for the first time the federal government is spending more money and now asking for results."

"If you don't test," he said, "you have a system that just shuffles the kids through and that's unacceptable. ... The national objective is to challenge the soft bigotry of low expectations and to raise the standards for every single child."

A White House statement said Bush's 2005 budget calls for an additional $1 billion in funding for disadvantaged students, $1 billion for special education programs, and $138 million for reading programs.

Bush called Westview an example of a school that has succeeded under the program. While the vast majority of students are from low-income families, tests scores in reading and math have gone up substantially in recent years.

Democrats said the act could help schools but is failing in its mission.

"While the ideals espoused in No Child Left Behind (NCLB) are admirable, the realities of the Bush plan are not," Dean wrote in the Seattle Times. "NCLB imposes rigid and expensive mandates on public schools. It judges adequate yearly progress using a one-size-fits-all formula, a measure that gives schools an incentive to lower testing standards in order to meet federal requirements and, sadly, to push out students that may bring down a school's average score."

More than a quarter of U.S. schools did not make "adequate yearly progress" under the program in 2003 and don't have the support they need to improve, Dean said. "It is absolutely unconscionable for the president to demand that states pay for federally required programs without properly funding them. Since NCLB passed, we have been hearing horror stories from states desperately looking for money to meet requirements."

Opting out of federal funds

Some school districts are opting out of the federal funds available under the act rather than trying to meet the standards.

Dean said the act can be reformed to invest in schools and judge progress by means other than standardized tests.

Rep. Harold Ford Jr., D-Tennessee, said he hoped that while visiting his state Bush would "listen carefully to some of the educators and parents and superintendents and school board members who are living the reality of implementing No Child Left Behind. In theory, it's a great bill. ... But in practice, we're not fully funding it. It's not allowing teachers and school districts the flexibility needed to teach kids."

Under the No Child Left Behind Act, states are required to test every child's progress in reading and math in third through eighth grades and at least once during 10th through 12th grades. By school year 2007-2008, testing in science also will be required.

Schools must show adequate yearly progress, and states must issue annual report cards on school performance and statewide test results.

After five years, schools that fail to show adequate yearly progress must be restructured. Such a move could include reopening the school as a charter school, replacing most or all of the staff or turning the school over to the state or a private company.